This is a long-term study of the several components of the cell surface of streptococci and of their role in the pathogenesis of disease. Each of the external limiting structures of group A streptococci - the capsule, the cell wall, and the cytoplasmic membrane-are included in these investigations. The ultimate goal is to elucidate the mechanisms involved in pathogenesis of the major sequelae of streptococcal infections: rheumatic fever and glomerulonephritis. To this end, special emphasis is now placed on the nature and biological properties of the antigens of the cytoplasmic membrane because of the demonstrated cross-reactivity between components of this structure and mammalian tissue antigens.